One form of apparatus for applying an imprint to a web of flexible material by means of a stamping foil which can also be referred to as an embossing or transfer foil, as is to be found for example in DE 32 10 551 C2, compises a stamping or foil-applicator roller and at least one and more specifically a plurality of pressure or backing rollers, by means of which the foil and the web of material can be pressed against each other and against the peripheral surface of the stamping roller. In that assembly the backing rollers are disposed combined together in pairs on a respective roller cage. The backing rollers can be individually adjusted, in such a way that firstly one or two adjacent inner backing rollers and then progressively outwardly the further backing rollers can be brought to bear against the stamping roller. However, particularly when that apparatus is being used to deal with webs of flexible delicate or sensitive material such as for example banknote paper, it is not possible with certainty to exclude the likelihood of undesirable compression of the fibers of the material and thus an undesirable change in the properties of the material, as a result of the material being subjected to pressure over the full area thereof between the backing roller and the stamping or applicator roller.
In another form of apparatus, to be found in DE 40 24 537 C1, for applying a foil imprint to a web of flexible material, the aim therein is to avoid undesirable compression of the fibers of the material and thus an unacceptable change in the properties thereof, even when dealing with a web of flexible material to which a stamping or transfer foil imprint is to be applied, without the operating speed of the apparatus being adversely affected by the avoidance of fiber compression and its consequences. That aim is achieved by the at least one backing roller being provided with an adjusting device for producing defined adjustment of the spacing of the backing roller relative to the surface of the stamping or applicator roller, thereby to provide for defined adjustment of the pressure applied by the backing roller to the foil and the web of material.
However, tolerances in respect of thickness of the web of material and/or flaws in respect of shape caused by temperature conditions, for example out-of-roundness of the stamping or applicator roller, caused by a temperature variation, can result in irregular depths of impression of the at least one backing roller into the web of material, thus resulting in an irregular imprint effect.